The invention relates to a high-efficiency amplifying device.
High-efficiency amplifying devices as such have been known for some time, particularly if they are embodied as so-called class F amplifiers, e.g. see also "Solid State Radio Engineering" by Kraus and Bastian, John Wiley and Sons, New York, Section 14-4 Class F Amplification. It is essential for amplifiers with class F operation that resonance devices for a basic frequency and at least one harmonic be connected on the output side. As a rule, only twice or three times the basic frequency is used as a harmonic (e.g., RF Design, May 1996, pp 79-84: "An Introduction to class F Power Amplifiers" by F. H. Raab).
High-efficiency amplifying devices are of particular interest for accumulatoroperated or battery-operated devices with high frequencies, such as mobile telephones, so as to allow for long operating times with the limited energy supply.
A high-efficiency amplifying device for the 8-GHz band is described in the IEEE MTT-S Digest 1996, pp 689-692. For this device, a trapeze-shaped half-wave signal is generated in a pre-amplification stage, located in front of the power amplifying unit, from a sine-shaped input signal as a drive signal for the power amplifying unit, meaning a field-effect transistor. The 3.sup.rd and the 5.sup.th harmonic, 3fo and 5fo, are used in addition to the basic frequency in order to generate the trapezoid shape. In the report "High Efficiency Harmonic Control Amplifier" by Ingruber, Pritzel and Magerl, delivered during the IEEE MTT-S Intern. Symposium on Microwaves 1996, an amplifying device is described in which signal shares are generated in a preselection stage during the 2.sup.nd harmonic in addition to the basic frequency from the input signal. These signal shares are used for the drive signal to achieve an approximately half-wave shape for the drive signal.
Arrangements with harmonics in the drive signal of the power amplifying unit have the advantage that a high degree of efficiency is achieved without over-modulating the power amplifier.
The disadvantage of devices with harmonics in the drive signal of the power amplifying unit is the appearance of intermodulation products in the output signal, resulting from generated harmonics. The intermodulation products in the basic frequency cannot be suppressed by the basic-frequency band-pass filter on the output side.
U.S. Pat. No.-A-3,755,754 discloses a high-efficiency amplifying device, in which a drive signal for an active power amplifying unit is derived in a preselection stage from an input signal, in such a way that the drive signal contains signal shares for the basic frequency of the input signal and the at least one harmonic of this basic frequency, wherein the amplification characteristic of the preselection stage has an inverse phasefrequency characteristic to the power amplifier for the basic frequency.
A high efficiency amplifying device is also known from EP-A 0 252 364 where the amplification characteristic of the preselection stage has a signal-expanding course for the signal share in the basic frequency.
It is the object of the present invention to provide a high-efficiency amplifying device, which supplies good signal amplification with low disturbance and high linearity while requiring little expenditure.